Question

What is meant by work done by a force? When do we call work done to be positive or negative? In a game of ‘tug of war’, state the type of work done by the winning and the losing team?

Answer 1

1. Work is said to be done on an object by a force if the object moves a certain distance.
2. Work done can be calculated as-
   $$\begin{gathered} W=\left(F\cos \theta \right)\times s \\ HereW=worddone\left(j\right) \\ F=forceapplied\left(N\right) \\ s=displacement\left(m\right) \\ \theta =anglebetweenFands \end{gathered}$$
3. Work done will be positive or negative that will depend on the value of $\theta$.
4. If the value of $\theta =0^{°}$the work done will be positive.
5. If the value of $\theta ={180}^{°}$the work done will be negative.

In a game of tug of war-
a) Work done by losing team-

1. In the game of tug of war losing team applies force in the direction opposite to the direction of motion.
2. Therefore the angle between force and displacement is 180⁰.
3. Since cos 180⁰= -1.
4. $$\begin{gathered} W=\left(F\cos {180}^{°}\right)\times s \\ W=-(F\times s) \end{gathered}$$
5. Hence in a tug of war work done will be negative by the losing team.

(b) Work done by the winning team:

1. In the game of tug of war, the winning team applies force in the direction of motion.
2. Therefore the angle between force and displacement is 0⁰.
3. Since cos 0⁰=1
4. $$\begin{gathered} W=\left(F\cos 0^{°}\right)\times s \\ W=F\times s \end{gathered}$$
5. Hence in a tug of war work done will be positive by the winning team.